The invention is a system and a method for controlling boundary layer flow over a surface such as that formed by an airfoil, interior of a duct, or other fluid flow surfaces.
There is a long standing and continuing need, in industries concerned with fluid flow dynamics, for an effective means to control boundary layer flow conditions. The energy required to operate a particular fluid flow system is directly related to the flow conditions in the boundary layer. In fact, successful system operation may be dependent on boundary layer flow conditions. For example, an airfoil set at particular operating conditions may stall and fail to achieve useful lift when boundary layer flow is laminar, yet can continue to operate under those same conditions if turbulent flow is established in the boundary layer. Even where a system can operate successfully without boundary layer control, such control will provide significant benefits. Typically, skin friction drag may be reduced by one-third just by partially suppressing turbulent oscillations in the boundary layer.
Engineering efforts and techniques directed toward boundary layer control have been extensive and in many gases. The spectrum of techniques has spanned active and passive methods, from high energy air injection or withdrawal to vortex generators and shaping of micro-geometries. The more effective techniques have been hampered by cost, power and weight requirements, mechanical complexity and unreliability. Potentially more attractive systems, such as surface micro-geometries, vortex generators and other passive methods, have provided limited results while incurring penalties of their own. Vortex generators, for example, are typically point-designed for a particular configuration, e.g., flaps down and a particular operative point. At other operating points, vortex generators create drag and icing problems while making no contribution.
Accordingly, it is an object of the present invention to provide an active means of boundary layer control wherein both transition and disturbances are controlled.
It is a further object of the present invention to reduce skin friction drag through active boundary layer control.
It is yet another object of the present invention to provide extended stall characteristics to an airfoil through turbulent boundary layer control.
A further object of the present invention is to provide an active boundary layer control system which has low power and weight requirements.
Yet another object of the present invention is to provide non-intrusive control means wherein the apparatus is flush or internal to the flow surfaces.
Still another object of the present invention is to provide localized effects which can be tailored in amplitude and frequency to match local flow conditions.
It is yet a further object to provide a boundary layer control system which is reliable and mechanically simple.
A further object of the present invention is to provide for boundary layer control by triggering flow transition with heating elements and by damping flow oscillations with audio speakers.